Page 118 - NAME OF CONDITION: REFRACTIVE ERRORS

The first technical problem that confronts the surgeon is placement of the infusion cannula.
Because the media is almost always too cloudy for the surgeon to be able to visualize a pars

plana port, this infusion cannot be used for the initial stages of the operation. Because the
incision and placement of the infusion port are easier in a firm eye, it is often worthwhile
placing an inferotemporal port with sutures, reserving its use for later in the procedure,
once the location of the tip in the vitreous cavity can be verified.

The presence of the crystalline lens or a pseudophakos will determine placement of the
canula (3.5mm from limbus in pseudophacos, 4mm in phakic eyes). If light is not needed
during the initial portion of the procedure, a bent needle or other blunt infusion canula can
be positioned in the center of the pupillary space, where its position can be monitored.
This infusion can be turned on at this stage so that the incision through the pars plana for
the cutting instrument may be made in a firm eye. The anterior chamber often contains
significant amounts of fibrin and hypopyon. Because the cornea invariably has some
combination of epithelial edema, folds, and cells deposited on the posterior surface, the iris
and central anterior vitreous are often impossible to visualize adequately. Initial incisions
may be made in the limbus at approximately the 9.30 and 2.30 clock positions, modifying

the location as necessary depending on the condition of the previous surgical wound and
on the presence of a filtering bleb. Fluid is infused into the anterior chamber as
inflammatory debris is removed with the suction and cutting instrument. If an
inflammatory membrane extends over the iris surface and the lens, a bent needle can be
used to gently peel it off the surface. The vitrectomy is now progressively carried
posteriorly. The vitreous removal is performed initially in the center of the vitreous cavity.
Pockets of more heavily infiltrated vitreous are sometimes located; in the aphakic eye,
peripheral depression may be used to bring these into view. Aggressive removal of all

infiltrated vitreous in the basal area should not be attempted because this often results in
retinal tears. The presence of a posterior vitreous detachment, on the other hand, allows
more complete vitreous removal. If the vitreous is still attached, a judgment must be made
about the amount of vitreous to be removed. The cutting of vitreous adjacent to inflamed
or necrotic retina will often cause retinal breaks; these are difficult to seal and may result in
failure of the case. In eyes with posterior vitreous detachment, a white mound of
inflammatory debris may be visible over the posterior pole. This should be approached
with care and may be gently aspirated into the cutting port. If the mound proves to be solid
and adherent, small amounts can usually be removed, but in most cases it is unwise to
attempt to remove large portions. In some instances the material is flocculent and
equivalent to an unorganized hypopyon; this can be gently sucked up with vacuum

techniques. The procedure is completed by closing all incisions in a watertight manner and
injecting intraocular antibiotics. After closure of the conjunctival incisions, subconjunctival
antibiotics are often injected.

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